1. Field of the Invention
The present invention relates to a game machine having a variety of prize modes and, more particularly, to a game machine having a function to make a change to a game state, in which a predetermined prize mode is easily concentrated, when a predetermined condition is satisfied.
2. Related Art
Conventionally, the game machine equipped with such various prize modes is prepared to have a plurality of prize modes of low bonuses (as will be called the "low bonus modes") and a plurality of prize modes of high bonuses (as will be called the "high bonus modes") so that any of these low bonus modes and high bonus modes may be selected by a random number lottery.
For each prize mode, on the other hand, the lottery probabilities and the bonus numbers are predetermined according to the bet numbers so that the game can be played within a range of the expected value which is determined by those bet number, lottery probability and bonus number. Here, the expected value indicates how many coins can be expected for each coin inserted for a game.
There are further prepared a game state set to a relatively low expected value RL (as will be called the "ordinary probability game state") and a game state set to a higher expected value RH than that of the ordinary probability game state (as will be called the "high probability game state"). If a predetermined condition is satisfied during in a play in the ordinary probability game state, the game state is changed to the high probability game state so that a predetermined prize mode is concentratively prized to give the high expected value RH to the player.
For example, the conventional slot machine is prepared to have the prize modes which are called a big bonus game (as will be called the "BB game"), a regular bonus game (as will be called the "RB game") and a single bonus game (as will be called "SB game") as the high bonus modes, and a small mode such as "Replay", "Bell" or "Bullet" as the low bonus modes.
On the other hand, there are prepared a prize decision table for the ordinary probability game state, which is stored with data of lottery probabilities a1to a6and bonus coin numbers M1to M6assigned to the respective prize modes, as shown in FIG. 1A, and a prize decision table for the high probability game state, which is stored with data of the lottery probabilities a1, a2, a3, a4to a6and the bonus coin numbers M1to M6assigned to the respective prize modes, as shown in FIG. 1B. The expected value RL in the ordinary probability game state and the expected value RH in the high probability game state are determined on the basis of the following Formulas (1) and (2): EQU RL={(a1.times.M1)+(a2.times.M2)+(a3.times.M3)+(a4.times.M4)+(a5.times.M5)+( a6.times.M6)}.div.T (1);
and EQU RH={(a1.times.M1)+(a2.times.M2)+(a3.times.M3)+(a4.times.M4)+(a5.times.M5)+( a6.times.M6)}.div.T (2);
Here in Formulas (1) and (2): T indicates the bet number; a1to a6and A3indicate the lottery probabilities for the respective prize modes; and M1to M6indicate the bonus coin numbers for the respective prize modes. For the "SB game", on the other hand, the lottery probability a3in the ordinary probability game state and the lottery probability A3in the high probability game state are set in a relation of A3=10.times.a3, from which the expected values RL and RH are related to RL&lt;RH.
During a game in the ordinary probability game state, the random number lottery for a prize mode is performed on the basis of the prize decision table shown in FIG. 1A.
If a predetermined condition is satisfied during a game in the ordinary probability game state, on the other hand, the high probability game state is established by making a change to the prize decision table, as shown in FIG. 1B. As a result, the probability, at which the "SB game" is randomly lotted, i.e., the lottery probability is raised from a3 to A3(=10.times.a3) so that the "SB game" is concentratively won to provide a game of the high expected value RH for the player.
In the conventional game machine thus far described, the expected value RH in the high probability game state is enhanced by raising only the lottery probability for a specific prize mode such as the aforementioned "SB game" when the game state is switched from the ordinary probability one to the high probability one. In the respective prize decision tables shown in FIGS. 1A and 1B, more specifically, the expected value is enhanced from RL to RH merely by raising the lottery probability for the "SB game" from a3to A3.
If the expected values RL and RH are set by those means, however, the expected value RH in the high probability game state may exceed a predetermined proper expected value Rmax (e.g., 0.9) to raise the so-called "payout ratio" so excessively that no proper game mode cannot be provided for the player thereby to impose a heavy economical burden on the game house.